Elimination of room-temperature brittleness of Fe-Ni-Co-Al-Nb-V alloys by modulating the distribution of Nb through the addition of V

Compared with Ti-Ni-based and Cu-Al-based alloys, Fe-Ni-Co-Al-based superelastic alloys have received great attention in recent years because of their low cost and excellent performance. However, the precipitation of brittle precipitates on grain boundaries in Fe-Ni-Co-Al-based polycrystalline alloys significantly reduces the mechanical properties. In this paper, the effects of V on the formation of brittle precipitates on both grain boundaries and inside grains and mechanical properties in Fe-Ni-Co-Al-Nb alloy were investigated systematically. The results show that gamma '(Ni3Al) precipitate with L1(2) structure precipitate out on grain boundaries and inside grains in the Fe-Ni-Co-Al-Nb alloy during aging without V addition. The gamma ' precipitate with L1(2) structure on the grain boundaries grew to form a heavily-coarsened L1(2) precipitate (HCLP gamma ' precipitate) due to the accumulation of Nb on the grain boundaries, resulting in a significant decrease in elongation. With the addition of V, intragranular Nb and V can combine together with gamma ' to form Ni-3(Al, Nb, V) (nano-sized gamma ' precipitate) composite precipitates, which improves the strength. More important, since the diffusion coefficient of V was larger than that of Nb, V preferentially occupied the lattice positions on grain boundaries, repelling Nb from the grain boundaries to the matrix. Thus, the coarsening of HCLP gamma ' precipitate on the grain boundaries was reduced, and the elongation of Fe-Ni-Co-Al-Nb-V alloy was significantly improved.

Automated summary

This paper systematically investigated the effects of V on the formation of precipitates and mechanical properties in Fe-Ni-Co-Al-Nb alloy. It was found that the addition of V can improve the strength by forming nano-sized gamma' precipitates, and significantly improve the elongation of the alloy.